Creating a mongodb capped collection in java

问题:

I want to create a capped collection from Java code. I found the syntax for creating it through JavaScript, but could not find an example for Java.

Mongo mongo = new Mongo("127.0.0.1");
DB db = mongo.getDB("mydbid");

DBCollection collection;
if (db.collectionExists("mycollection")) {
        collection = db.getCollection("mycollection");
    } else {
        collection = /* ????? Create the collection ?????? */
    }
}

回答1:

Use the DB.createCollection operation and then specify a DBObject that has capped as a parameter. You can then specify size and max in order to control the byte size and the maximum number of documents. The MongoDB site has a tutorial on capped collections that explains all the options, but is missing an example for each driver.

Mongo mongo = new Mongo("127.0.0.1");
DB db = mongo.getDB("mydbid");

DBCollection collection;
if (db.collectionExists("mycollection")) {
        collection = db.getCollection("mycollection");
    } else {
        DBObject options = BasicDBObjectBuilder.start().add("capped", true).add("size", 2000000000l).get();
        collection = db.createCollection("mycollection", options);
    }
}

回答2:

With more recent java mongo driver (ie 3.4) the creation should slightly change:

CreateCollectionOptions opts = new CreateCollectionOptions().capped(true).sizeInBytes(1024*1024);
database.createCollection("test", opts);

Please, notice that the createCollection is not returning any value.